Fluid pressure hammer



Oct. 3, 1933. E. w. sTEvENs FLUID PRESSURE HAMMER Filed sept. 25. 192:3V

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Patented Oct. 3, 1933 y Visza'uww Y n .FLUID rREssUREjnAm/IER. Edward W.V Stevens, Detroit, Mich., asisignor to Chicago Pneumatic .Tool Company, vNew York, N. Y., a corporationof New Jerseyv VApplication September'25, 1928 Serial No.308,205 l z'olaims," (011121-261 v This invention relates to percussive tools op.-

erated by fluid pressure and commonly referred to as pneumatic or air hammers. Moreparticularly it relates to pneumatic toolsV having automatically thrown valves and to the manner of controlling the distribution of the pressure fluid.

' One object of fthe invention is to provide a tool of the described type characterized by simplicity of construction and high operating eiciency. An-

,10 other object is to'eliminate constant pressure ports which tend to shift the valve prematurely. Another object is to avoid 'unnecessary waste of motive fluid. Other objects will be apparent from the detailed description which follows. Y

The objects of the invention are accomplished by constructing the valve with carefully calculated proportions in connection with ports and passages so arranged that the effective workng pressures .tending to movethe valve in the desired direction will be opposed only by a slight difference in the holding force, thus producing a necessarily rapidshiftng of the valve at the proper instant; The valve preferably has only three diameters and four effective working surfaces or areas subjected to the pressure fluid.

In order to illustrate the invention, one concrete embodiment thereof is shown in the accompanying drawing, in which:

Fig. 1 is a side elevational view largely in section; and

Fig. 2 is a fragmentary sectionalA view similar to Fig. 1 but with the lower part taken at a different angle to provide a section through one of the exhaust ports, the view showing the valve Vand piston in different positions from those shown in Fig. 1.

'I'he embodiment of the-invention, chosen for the purpose of illustration, comprises a pneumatic riveting hammer having a cylinder 3 pro- 40 viding a piston chamber 3a in which reciprocates a hammer piston 4 arranged to deliver its blows to a suitable working tool such as a rivet set 5 retained in the outer end of the cylinder by a rivet set clip 6. The rear end of the cylinder is closed by a handle 7 having an extension 'lain threaded engagement with the exterior of cylinder 3. Securely clamped within a. counterbore 3b of` cylinder 3 by the handle is a valve case part 10a, a slightly larger diameter part 10b at therear, and a substantially central flange 10c. The valve accordingly has but four pressure areas, namely, the two extreme ends of the valve and the two faces of. fiange 10c.

, In Fig.' 1, valve 10 has just shifted forwardly and piston 4 is beginning `its forward or Working stroke.Y ,Motive fluid entering the hammer through the handle duct 7b passes into the rearwardend of the valve case through an annular series ofV passages .11 communicating with an annular groove 11a which in Fig. 1 is uncovered by the valve 10 to admit the motive fluid directly into the rear end ofthe piston'chamber. With piston 4 in the position shown, this motive fluid has access to the pocket rearwardly of the piston througha restricted passageor by-pass 12. The airV trapped in front` Vof Vthe piston is vented to` atmosphere through. one or `more passages 13 communicating by'ports 13a with the chamber rearwardly of flange 10c of the valve whence the air passes to atmosphere through ports 14a (Fig. 2) communicatingvwith a series of passages 14 extending to atmosphere. Just before piston'4 delivers its blow to the rivet set 5, it uncovers a port 15a communicating with an axial shift passage 15 which directs pressure fluid from the piston chamber through a greatlyV restricted port 15b directly against the forward face of the valve flange 10c. This face or valve area exceeds the area provided by the rearward edge of the valve and although the port 15b is very small the cham- Vber with whichV it communicates is small also with the result that rearward movement of the valve is promptly initiated. Shortly after its initial movement, flange 10c of the valve uncovers a live air port 16a which is supplied with motive fluid through a passage 16 communicating with one of the live air passages 11. The live air admitted by port 16a augments the pressure fluid supplied through restricted port 15b and moves `the valve promptly to the rearward position shown Vwhereby the live motive fluid admitted to the chamber forwardly of valve flange 10c by port 16a has access through passages 13 to the forward end of the piston chamber to drive the piston rearwardly. The small size of port 15b of shift passage 15 prevents any appreciable loss of motive compressed air acts against the rearward edge of valve 10 and continues to have access thereto even after piston 4 has passed beyond the valve byA means of passage 12 (Fig. l). In the meantime, piston 4 on its rearward movement has uncovered port 15a thereby assisting, through shift passage 15 and restricted port 15b, in reducing ther pres-- sure inthe valve chamber forwardly of flange .10c

to that obtaining in the forward piston chamber.l

As a consequence, the pressure against the rearward edge -of the valve preponderates and the valve moves forwardly to the position' shown inl Fig. 1, thus completing the cycle of operation. y

The restriction of the port '15b is a noveland essential feature' of the present invention and results from the discovery thata restriction in the shift passage at this point, namely, immediately adjacent the valve is sufficient to 'initiate shifting movement of the valve by the high velocityjet of air entering a Very restrictedvr chamberand impinging directly.r against'th'e valve.4 The shifting of the valve may be completed by live air admitted through a port such as 16a uncovered bysuch,

initialimovement of ythe-valve and the restriction of the shift, passage can be made sufficient to avoid any tendency of the valve to flutter by reducing l the amountl of air which can escape into the piston chamber.

It also has the effect of greatly reducing the air consumption of the hammer since the amount of live air which can escape through restricted port 15b and out into'th'e piston chamber Abetweenv the ltimevwhen they valve shifts and portv 15a is covered by piston 4 and' after piston 4 passes beyond port V15a and before the valve shifts to the forward position is so small as to be practically negligible. In a standard riveting hammer having a nine inch stroke, the

shift passage v15 is a 5/32 drill hole while the restricted port 15 is a 1/16l drill hole. This makes the cross sectional area of the restricted port only 4/25 or less than 1/5 the area of the shift passage.

' While the invention has been herein disclosed in what is now considered to be a preferred form, it is vtobe understood that the invention is not restricted to thespecific details thereof but covers all changes, modifications, and adaptations within the scope of the appended claims.

" lI claim as my invention:

'1, A Ifluid pressure. tool comprising a cylinder,

a piston reciprocable therein, a valve for controlyling the distribution of the motive fluid and moving in timed relation with said piston, said valve having-a flange, means for admitting motive fluid 'Y to oneface of said flange to move the valve in one "direction comprising a passage controlled by said piston, said passage terminating in a greatly restricted portv immediately adjacent said valve flange, means controlled by said flange to admit live motive fluid to complete the shifting movement of said valve, and'passages uncovered by said valve flange for utilizing the motive fluid admitted by said last-named means for effecting the rearward stroke of said, piston.

2.v A fluid pressure tool comprising a cylinder, a piston reciprocable therein, a valve for controlling the distribution of motive fluid Vand moving in timed relation with said piston, said valve havingv a shift area, meansl forn admitting pressure iluidtosaid area to move the valve in one direction comprising a passage controlled by said piston, said passage opening against said areaV by a. port whose cross sectional area is one-fifth or less the varea of said passage, means uncovered by said valve'to admit liver motive fluid to said area to complete the shifting movement Vof said valve, and means'controlled by said valve and utilizing live motive yfluid admitted by said last named means to said valve area for effecting the rearward stroke of said piston.

' EDWARD W. STEVENS. 

